DESCRIPTION

These functions return information about a file. No permissions are
required on the file itself, but — in the case of stat() and lstat() —
execute (search) permission is required on all of the directories in
path that lead to the file.
stat() stats the file pointed to by path and fills in buf.
lstat() is identical to stat(), except that if path is a symbolic link,
then the link itself is stat-ed, not the file that it refers to.
fstat() is identical to stat(), except that the file to be stat-ed is
specified by the file descriptor fd.
All of these system calls return a stat structure, which contains the
following fields:
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode number */
mode_t st_mode; /* protection */
nlink_t st_nlink; /* number of hard links */
uid_t st_uid; /* user ID of owner */
gid_t st_gid; /* group ID of owner */
dev_t st_rdev; /* device ID (if special file) */
off_t st_size; /* total size, in bytes */
blksize_t st_blksize; /* blocksize for filesystem I/O */
blkcnt_t st_blocks; /* number of blocks allocated */
time_t st_atime; /* time of last access */
time_t st_mtime; /* time of last modification */
time_t st_ctime; /* time of last status change */
};
The st_dev field describes the device on which this file resides.
The st_rdev field describes the device that this file (inode)
represents.
The st_size field gives the size of the file (if it is a regular file
or a symbolic link) in bytes. The size of a symlink is the length of
the pathname it contains, without a trailing null byte.
The st_blocks field indicates the number of blocks allocated to the
file, 512-byte units. (This may be smaller than st_size/512 when the
file has holes.)
The st_blksize field gives the "preferred" blocksize for efficient file
system I/O. (Writing to a file in smaller chunks may cause an
inefficient read-modify-rewrite.)
Not all of the Linux filesystems implement all of the time fields.
Some file system types allow mounting in such a way that file accesses
do not cause an update of the st_atime field. (See "noatime" in
mount(8).)
The field st_atime is changed by file accesses, for example, by
execve(2), mknod(2), pipe(2), utime(2) and read(2) (of more than zero
bytes). Other routines, like mmap(2), may or may not update st_atime.
The field st_mtime is changed by file modifications, for example, by
mknod(2), truncate(2), utime(2) and write(2) (of more than zero bytes).
Moreover, st_mtime of a directory is changed by the creation or
deletion of files in that directory. The st_mtime field is not changed
for changes in owner, group, hard link count, or mode.
The field st_ctime is changed by writing or by setting inode
information (i.e., owner, group, link count, mode, etc.).
The following POSIX macros are defined to check the file type using the
st_mode field:
S_ISREG(m) is it a regular file?
S_ISDIR(m) directory?
S_ISCHR(m) character device?
S_ISBLK(m) block device?
S_ISFIFO(m) FIFO (named pipe)?
S_ISLNK(m) symbolic link? (Not in POSIX.1-1996.)
S_ISSOCK(m) socket? (Not in POSIX.1-1996.)
The following flags are defined for the st_mode field:
S_IFMT 0170000 bit mask for the file type bit fields
S_IFSOCK 0140000 socket
S_IFLNK 0120000 symbolic link
S_IFREG 0100000 regular file
S_IFBLK 0060000 block device
S_IFDIR 0040000 directory
S_IFCHR 0020000 character device
S_IFIFO 0010000 FIFO
S_ISUID 0004000 set UID bit
S_ISGID 0002000 set-group-ID bit (see below)
S_ISVTX 0001000 sticky bit (see below)
S_IRWXU 00700 mask for file owner permissions
S_IRUSR 00400 owner has read permission
S_IWUSR 00200 owner has write permission
S_IXUSR 00100 owner has execute permission
S_IRWXG 00070 mask for group permissions
S_IRGRP 00040 group has read permission
S_IWGRP 00020 group has write permission
S_IXGRP 00010 group has execute permission
S_IRWXO 00007 mask for permissions for others (not in group)
S_IROTH 00004 others have read permission
S_IWOTH 00002 others have write permission
S_IXOTH 00001 others have execute permission
The set-group-ID bit (S_ISGID) has several special uses. For a
directory it indicates that BSD semantics is to be used for that
directory: files created there inherit their group ID from the
directory, not from the effective group ID of the creating process, and
directories created there will also get the S_ISGID bit set. For a
file that does not have the group execution bit (S_IXGRP) set, the set-
group-ID bit indicates mandatory file/record locking.
The sticky bit (S_ISVTX) on a directory means that a file in that
directory can be renamed or deleted only by the owner of the file, by
the owner of the directory, and by a privileged process.

RETURNVALUE

On success, zero is returned. On error, -1 is returned, and errno is
set appropriately.

ERRORS

EACCES Search permission is denied for one of the directories in the
path prefix of path. (See also path_resolution(7).)
EBADFfd is bad.
EFAULT Bad address.
ELOOP Too many symbolic links encountered while traversing the path.
ENAMETOOLONG
File name too long.
ENOENT A component of the path path does not exist, or the path is an
empty string.
ENOMEM Out of memory (i.e., kernel memory).
ENOTDIR
A component of the path is not a directory.

NOTES

LinuxNotes
Since kernel 2.5.48, the stat structure supports nanosecond resolution
for the three file timestamp fields. Glibc exposes the nanosecond
component of each field using names either of the form st_atim.tv_nsec,
if the _BSD_SOURCE or _SVID_SOURCE feature test macro is defined, or of
the form st_atimensec, if neither of these macros is defined. On file
systems that do not support sub-second timestamps, these nanosecond
fields are returned with the value 0.
For most files under the /proc directory, stat() does not return the
file size in the st_size field; instead the field is returned with the
value 0.
Underlyingkernelinterface
Over time, increases in the size of the stat structure have led to
three successive versions of stat(): sys_stat() (slot __NR_oldstat),
sys_newstat() (slot __NR_stat), and sys_stat64() (new in kernel 2.4;
slot __NR_stat64). The glibc stat() wrapper function hides these
details from applications, invoking the most recent version of the
system call provided by the kernel, and repacking the returned
information if required for old binaries. Similar remarks apply for
fstat() and lstat().